1. Field of the Invention
The invention relates to a heating device, more particularly to a heating device for a heat transfer medium, which heating device does not cause pollution and can prolong the useful life of the heat transfer medium.
2. Description of the Related Art
A roller assembly is normally employed to advance a plastic film product which is obtained from a conventional plastic film manufacturing process. The plastic film product is very thin, is at a relatively high temperature immediately after manufacture, and therefore requires gradual cooling so as to prevent adverse effects to the same. If the roller assembly was not heated to a desired temperature before the plastic film product was advanced, immediate contact between the plastic film product and the roller assembly would cause a rapid decrease in the temperature of the former, thereby resulting in unfavorable effects to the plastic film product.
In order to maintain the roller assembly at the desired temperature when advancing the plastic film product, the roller assembly is usually provided with a pipe member which extends therethrough. A circulating heat transfer medium (such as heat transfer oil) is heated by a boiler and flows through the pipe member. Conventional boilers are usually heated by coal or oil and are used to apply heat to the pipe member or to a reservoir containing the heat transfer medium. The heat transfer medium, which was heated by the boiler, flows through the pipe member and is returned to the boiler so as to be heated again.
The above described heating process has several drawbacks. The conventional coal or oil-fired boilers emit smoke and can cause air pollution. Furthermore, rapid heating and cooling of the heat transfer medium which flows through the pipe member can easily cause faster degradation of the heat transfer medium. That is, the heat transfer medium becomes viscous and resinous-like, making it difficult for the heat transfer medium to flow through the pipe member. Under such conditions, replacement of the heat transfer medium is therefore required. Frequent replacement of the heat transfer medium increases the production costs incurred and can cause frequent interruptions in the production process.